1. Field of the Invention
The present invention relates to a method of manufacturing a crystalline silicon base semiconductor thin film containing impurity required for formation of silicon semiconductors such as n- and p-type silicon semiconductors, which can be a material of silicon base transistors such as a c-MOS transistor used in integrated circuits such as a Large Scale Integrated Circuit (LSI).
2. Description of the Background Art
A method of manufacturing a crystalline silicon base semiconductor thin film in the prior art primarily requires three different steps. In a first step, an amorphous silicon thin film or a silicon thin film containing fine crystals is formed on a substrate, e.g., by a vapor phase composition method such as a thermal CVD method or a plasma CVD method. In a second step, the silicon thin film is subjected to recrystallization by a laser annealing method or a solid phase growth method, in which thermal processing is performed by a thermal processing furnace, a high-temperature lamp or the like. In a third step, impurity doping is performed by implanting impurity, which is required for formation of n- or p-type silicon semiconductor, into the crystalline silicon thin film formed in the second step, e.g., by an ion implanting method. Depending on the structure of the transistor, the third step may be performed before the second step.
As described above, the conventional method roughly requires the three steps, each of which requires a very expensive apparatus, resulting in increase in prices of final products. Accordingly, a manufacturing method, which requires a minimum number of steps, has been desired for producing inexpensive products.
Further, the foregoing conventional method suffers from the following problems.
In a process of producing a crystalline silicon thin film which will form, e.g., a base of a transistor, a substrate is heated to about 600xc2x0 C. when the solid phase growth method is performed as thermal treatment for recrystallizing the amorphous silicon thin film. In view of a resistance against thermal damages, therefore, a material of the substrate can be selected only from a restricted range, and the usable substrate material is restricted. In the laser annealing method, since adhesion between the substrate and the amorphous silicon thin film prepared by the vapor phase composition is low, the film is liable to be peeled off from the substrate when it is irradiated with laser beams, and further the particle diameters of crystals cannot be sufficiently controlled.
In the third step for doping the crystallized silicon thin film with impurity, e.g., by ion implanting method, a large number of lattice defects may occur in the film during ion implantation. Further, the crystals may be destroyed so that an amorphous layer may be formed.
Accordingly, it has been desired to provide a method, which can be used instead of the foregoing conventional manufacturing method, and can produce a semiconductor thin film having a good crystallinity and therefore a good quality at a low temperature.
As sizes of devices in Large Scale Integrated Circuits (LSIs) have been reduced in recent years, it becomes important to from an extremely shallow diffusion layer of impurity for semiconductor formation. Thus, reduction in size of the transistors has been required in accordance with miniaturization of devices in the LSI, and therefore it becomes important to determine a manner for adding impurity such as donor and acceptor forming the p- and n-type semiconductors into fine regions. For this impurity addition, a conventional ion implanting method has been improved to perform ion implantation with a low energy of 40 keV or less. However, it is impossible in the ion implanting method to prevent such a phenomenon (channeling effect) that the ions implanted into crystalline silicon move deeply through gaps between atoms of the crystals with a certain probability. When they move deeply, the impurity distribution exhibits a deep form having a long tail. Further, the ion implantation requires subsequent thermal treatment for activating the implanted impurity. During this thermal treatment, the impurity diffuses extremely fast in the tail portion of the impurity distribution due to reaction between the impurity and the defects which occurred during the ion implantation. Due to this, it is very difficult to form an extremely shallow diffusion layer having a high impurity concentration.
Accordingly, it is an object of the invention to provide a method, in which a crystalline silicon base semiconductor thin film can be manufactured inexpensively with a reduced energy, compared with the conventional method employing the three steps.
Also, an object of the invention is to provide a method, in which a crystalline silicon base semiconductor thin film having a good crystallinity and therefore a good quality can be manufactured at a low temperature.
Further, an object of the invention is to provide a method of manufacturing a crystalline silicon base semiconductor thin film, in which control can be performed to achieve a desired state of distribution, in a film thickness direction, of impurity required for silicon semiconductor formation.
The desired state of distribution is selected from a state in which the distribution is uniform in the film thickness direction, a state in which a distribution in an intended concentration is achieved at an intended portion in the film thickness direction and other states.
Further, an object of the invention is to provide a method of manufacturing a crystalline silicon base semiconductor thin film, in which the crystalline silicon base semiconductor thin film can be produced on a substrate together with an oxide thin film and/or a metal thin film layered thereto while suppressing external application of impurity onto a film boundary.
The invention provides a method of manufacturing a crystalline silicon base semiconductor thin film on a substrate, including the steps of:
forming a thin film primarily made of silicon on the substrate by forming plasma of a film material gas containing at least a silicon base gas at the vicinity of the substrate; and
crystallizing the silicon in the thin film primarily made of the silicon by emitting excited particles produced from an excited particle material gas to the substrate, wherein
at least one of the film material gas and the excited particle material gas contains an impurity gas for forming the silicon semiconductor, and thereby the crystalline silicon base semiconductor thin film is formed on the substrate.
According to the method of the invention, formation of the crystalline silicon thin film and addition of impurity which is required for formation of the silicon semiconductor in the thin film can be performed simultaneously by one device. Therefore, the crystalline silicon base semiconductor thin film can be manufactured inexpensively with a small energy, compared with the conventional method of manufacturing the crystalline silicon base semiconductor thin film employing the foregoing three steps.
Further, the crystalline silicon base semiconductor thin film having a good crystallinity and therefore a good quality can be manufactured at a low temperature.
In order to achieve the desired state (particularly, the positions and concentrations) of distribution of the impurity in the film thickness direction required for formation of the silicon semiconductor, within a predetermined time band during formation of the thin film primarily made of silicon, the amount(s) of the impurity gas(es) in the film material gas and/or the excited particle material gas may be controlled to take on predetermined value(s), respectively. In the case where the excited particle material gas contains the impurity gas (including the case where the excited particle material gas itself is the impurity gas), control may be performed in a time band during formation of the thin film primarily made of silicon, e.g., by emitting excited particles produced from the excited particle material gas to the substrate so as to achieve the desired state (particularly, the positions and concentrations) of distribution of the impurity in the film thickness direction required for formation of the silicon semiconductor.
The invention can also provide a substrate carrying a crystalline silicon base semiconductor thin film of a good quality together with an oxide thin film and/or a metal thin film, and prepared by successively forming, under predetermined gas pressures, the oxide thin film and/or the metal thin film as well as the crystalline silicon base semiconductor thin film in a layered fashion while suppressing external application of impurity onto a film boundary.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.